Saturday, May 31, 2014

This is a continuation of this series of posts, where we are analyzing long range climate model projections for the beginning of the winter of 2014-2015. This post will feature the CMC2 model.

The temperature forecast from the CMC2 model is a toasty one. We see warmer than normal conditions prevailing across the heavy majority of the country, especially around the Midwest and Northeast regions. There is a slight cooler than normal projection in the Southern Plains, but warmth definitely triumphs here. This forecast is very reminiscent of a typical El Nino temperature pattern, where warm weather stays in the North US and cooler than normal temperatures prevail in the South US. It would definitely be a welcome turn-around from what we experienced last winter.

The precipitation forecast for December 2014 from the CMC2 model is not as similar to an El Nino precipitation pattern. We see more or less neutral precipitation anomalies across the West Coast, but the real story is the shifting of drought-esque precipitation anomalies from the West to the Central US, as the CCM2 model predicts would happen to kick off the winter of 2014-2015. Typically, these dry anomalies would be centered in the Ohio Valley for an El Nino winter, not so far west. The El Nino pattern does briefly show itself as a wet start to winter in the East, but i'm not sold. I believe this model needs more time to solidify its forecast; I am not investing much confidence in it.

Lastly, we see the forecast of z200 anomalies for December 2014 from the CMC2 model. We're going to focus on the contour lines over the northern Hemisphere. In this forecast, we see the contour lines arching northward over the west coast of North America, signifying ridging/high pressure in that area. Typically, this would mean a chilly winter for the East US, but the arching of these contour lines extends east into the Central US, meaning high pressure would be favored over low pressure for that part of the country. This map does support the warm temperature forecast we saw earlier in this post, and such a forecast would be nearly a complete-180 from this past winter.Additional model forecasts will be discussed in the near future.Andrew

Wednesday, May 28, 2014

It is possible that an unusual Pacific ocean water pattern could increase the risk of a second straight cold winter.

Shown above are two composite images. The top row shows sea surface temperature anomalies during an El Nino event (top left), and during a La Nina event (top right). The bottom row shows sea surface temperature anomalies during a positive PDO event (bottom left), and during a negative PDO event (bottom right). You may notice that the images look similar. This is because typically, when there is an El Nino, below normal waters form in the North Pacific. Similarly, during a La Nina, warmer than normal waters tend to be observed in the northern Pacific. This is not a 100% correlation, it is just what usually happens. This year, we are seeing this correlation broken.

The above image shows observed sea surface temperature anomalies (SSTAs) on May 25th. We see two items of interest. The first is the presence of significantly above normal water temperatures in the northeast Pacific. This mechanism is what created sometimes-relentless bouts of ridging over the west coast of North America this past winter, greatly aiding in the cold weather that hit North America. This body of warm water still remains here this summer, and if it stays, may once again produce bouts of ridging resulting in a chilly winter for many in the United States.Going by the composite images at the top of this post, we would typically watch out for below normal water temperatures in the Equatorial Pacific, more specifically the waters west of Ecuador. However, that is not the case. We have been discussing the incoming El Nino for months now, which is allowing SSTAs in that area to rise. This means that we have warmer than normal waters in both the North Pacific and Equatorial Pacific, breaking the correlation we saw at the top of this post.So, what could that mean for winter? Let's find out.

The image above shows correlation values between surface temperatures in December-January-February (the winter season), and the observed Pacific-Decadal Oscillation (PDO). In other words, if the PDO is positive (see example in composite image at top of post), areas in positive correlation areas (warm colors) would see warmer than normal temperatures, since a positive PDO is positively correlated with surface temperatures. Inversely, a positive PDO being negatively correlated with surface temperatures means a positive PDO would result in colder weather for those in the negative correlation areas/cool color shades. Since these warm waters in the Northeast Pacific appear to be proclaiming a positive PDO regime right now, we could be in for a warm West US and very cold South/East US this winter if this correlation comes to fruition.

This image above shows correlations between the current El Nino or La Nina state, and surface temperatures across December-January-February. If we take positive water temperatures to mean El Nino, areas in the North and West US would see warmer than normal temperatures this winter, as an El Nino is positively correlated with surface temperatures. Similarly, a La Nina would bring colder weather to those Northern states. However, with the expected El Nino, we can expect warmth in the North and cold in the South, as the South is in that negative correlation area again. These two correlation comparisons can be put together to mean that a positive PDO and El Nino this winter may result in some very cold weather in the South and East US, with warmer temperatures stretched out across the North and West US.The PDO and El Nino are not the only two indices in the atmosphere, which may mean other factors may lessen this potential cold winter foreshadowing. We will get a better handle on this situation this summer and fall.Andrew

Tuesday, May 27, 2014

This is a continuation of this series of posts, where we are analyzing long range climate model projections for the beginning of the winter of 2014-2015. This post will feature the CMC1 model.

The temperature forecast from the CMC1 model, valid for December 2014, shows a very chilly winter for many in this country. This model suggests we will see an abundance of warm air overspreading Alaska and the west coast of North America. This is likely the result of high pressure, which then forces mid-level troughing to the east. This mid-level troughing, which will be discussed more later in this post, results in below normal temperature anomalies over the Central and East US, extending as far north as upper Canada. If you follow the weather closely, you may recognize this pattern as a positive Pacific-North American (PNA) index pattern. Like last winter, the Pacific pattern looks to have a grip on the downstream weather here in the US, resulting in a cold start to the winter.

The precipitation forecast from the CMC1 model shows a pattern almost identical to a traditional El Nino winter precipitation pattern. We first see anomalously wet conditions along the West Coast, a telltale El Nino signal due to the subtropical jet stream's natural enhancement due to the aforementioned El Nino. This enhanced subtropical jet stream then leads to more storm systems hitting the West Coast, and then more precipitation. We then see significantly below normal precipitation across the Central US, hitting the Ohio Valley the hardest. Once again, this is an El Nino signature. The El Nino is evident yet again in the CMC1 model's forecast for a very wet start to winter on the East Coast. This all strikes me as odd, since the temperature forecast does not reflect an El Nino temperature pattern, but given how this past winter went, you really have to expect the unexpected.

Lastly, we see the forecast of z200 anomalies for December 2014 from the CMC1 model. We're going to focus on the contour lines over the northern Hemisphere. In this forecast, we see the contour lines arching northward over the west coast of North America, signifying ridging/high pressure in that area. We discussed the likely presence of high pressure along the west coast earlier in the temperature forecast, and now we are seeing that theory come to fruition. We then see the contour lines plummet south over the Central US, which is how we got that cold December forecast at the top of this post. Oddly enough, we then see ridging in the Southeast US, which would typically divert storm systems north through the Ohio Valley. However, the precipitation forecast for the Ohio Valley is very dry, as shown above. This is likely the long range model up to its antics, which means confidence is similarly low.Additional models will be discussed in coming days.Andrew

Monday, May 26, 2014

I am still monitoring the potential for a period of active weather in mid-June.

The image above shows a long range forecast of outgoing longwave radiation (OLR) anomalies over the equatorial region of the globe, valid on June 14th. In both of these images, the yellows represent positive OLR, or suppressed tropical convection, while the blues denote negative OLR, or enhanced tropical convection. We can see a strong active Madden-Julian Oscillation (MJO) signal on the bottom panel, with deep blues indicating abnormal convection occurring over southern India into the waters east of the subcontinent. The placement of this enhanced convection tells me we are looking at a Phase 2 MJO, as the OLR composite shows below.

OLR anomalies for each MJO phase

Now, outside of the fact that Phase 2 MJO events have been known to increase the risk of violent tornado outbreaks in the spring months, the mid-level pattern during a June Phase 2 MJO event also signals the potential for severe weather.

The image above, produced by Americanwx, shows 500mb height anomalies over the northern hemisphere when the Madden-Julian Oscillation is in Phase 2 during the month of June. In this image, warm colors indicate high pressure/calm and warm weather, while cool colors denote stormy and cooler weather. During a typical MJO Phase 2 event in June, we tend to see ridging set up from the Bering Sea to the Great Lakes, enhanced slightly by weak troughing in the West. Because of this weak West US troughing, warmth and moisture are pumped north into the Central and East US from the Gulf of Mexico. This action then feeds into the increased potential for severe weather. Based on this composite, I do feel this time period may be defined by some active severe weather.

More evidence for an active severe weather period in mid-June arises when we take a look at the long range CFS severe weather forecast. The dates on the right display the date the forecast was made on, and the dates on the bottom legend indicate when this forecast is valid for. Warmer colors indicate the higher potential for severe weather. For instance, if I want to know the severe weather potential for May 30th on a forecast made on May 5th, I go up the legend on the left to find May 5th, then scroll on the corresponding horizontal line to find the May 30th box. In this case, we have been seeing the majority of recent forecasts highlighting the June 10-25 period as the one to watch out for, as the varying-colored boxes show on the upper-right corner of this image. Sometimes, there is safety in numbers in the weather world. In this case, with the relative consistency of these forecasts for the mid-June timeframe, I feel comfortable raising the concern of a potential active period for the aforementioned timeframe.

Wednesday, May 21, 2014

It does look like the positive phase of the Quasi-Biennial Oscillation is ending as we progress into summer, a move that may herald a cooler than normal upcoming winter. The Quasi-Biennial Oscillation (QBO) is an oscillation measured by the direction and intensity of winds in the middle of the stratosphere, usually around the 30 millibar level. When the QBO is in its positive phase, winds are called 'westerly', as they flow from west to east at an anomalously high speed. The positive QBO typically strengthens the polar vortex, thus resulting in a warmer than normal winter for lower latitudes. The negative QBO is when winds at the 30mb level are 'easterly', or going from east to west. Since this is the opposite direction as typical low pressure circulation in the Northern Hemisphere, the polar vortex is weakened, and cold weather tends to permeate the lower latitudes more frequently in the winter. Going by this, it would be plausible to associate this weakening +QBO with what could be a destabilized polar vortex next winter. This may mean additional opportunities for the polar vortex and associated cold weather air masses to penetrate deep into the United States, as they did last winter.

I discussed how my analogs for the upcoming winter showed upper latitude blocking, a feature that would be enhanced with the presence of a neutral, or more likely weak negative QBO phase. At this point, it is too early to tell whether we will be in a definitively negative QBO or a neutral QBO next winter, but the general concept of the weakening +QBO is clear, and this could be another element to a chilly winter ahead.

Saturday, May 17, 2014

This is a series of posts that I have made in previous years, in which I display a specific long range model and its prediction for the upcoming winter. Based on its success in past years, I have decided to kick off the multi-month series early, to give you an early heads up on the upcoming winter.Today's model will be the NASA model.

The above image shows the NASA model's forecast of 200mb wind speed anomalies across the world, with 200mb pressure contour lines superimposed. We want to mainly pay attention to the contour lines for today's analysis, since it seems to be the easiest for many to decipher over the anomalies. If we look at North America, we see the contour lines arching up across the West Coast, likely indicative of the presence of high pressure/ridging. This ridging over the western portion of North America then leads to a depression in the contour lines, where cold air would funnel southward into the central and eastern portions of the continent. This cold air would be helped along south by that troughing/depression in the contour lines. In other words, going solely by this image from this single model, we would be looking at a very similar set-up as last winter, with warmth over the West and cold over the East.

If we look at the North American temperature forecast for December 2014, the same timeframe as the image above, we see a similar story to my analog package which I posted about earlier this week. We see cold weather present across the South US, with warmth prevailing over Canada and the North US. This temperature forecast looks very similar to a textbook El Nino event, which is expected to form this summer and result, possibly, in a temperature pattern similar to the one above for this winter.

Lastly, the temperature forecast from the NASA model, valid December 2014, confirms the idea of a textbook El Nino pattern. We can recognize this El Nino pattern by viewing the below-normal precipitation across the Great Lakes and Ohio Valley, with a very wet precipitation pattern swallowing the Southeast and East Coast. These two features are common during an El Nino winter, and may very well appear this winter. On the West Coast, in accordance with the ongoing drought, we see well-below-normal precipitation values extending from California to Washington. All in all, even though this is a long range forecast, this solution is indeed a plausible one from this model.To summarize, the NASA model is predicting the following conditions to begin the winter of 2014-2015:• Cool South US• Warm North US• Wet & Stormy East Coast, Dry West Coast• Very similar to a typical El Nino patternAndrew

Wednesday, May 14, 2014

I'm seeing an increased probability for a severe weather event, potentially an outbreak, for the middle of June.

The image above shows a long range forecast of outgoing longwave radiation (OLR) anomalies over the equatorial region of the globe. In both of these images, the yellows represent positive OLR, or suppressed tropical convection, while the blues denote negative OLR, or enhanced tropical convection. We can see a strong active Madden-Julian Oscillation (MJO) signal on the bottom panel, with deep blues indicating abnormal convection occurring over southern India into the waters east of the subcontinent.

If we take a look at MJO composites for each phase, with blues once again defining enhanced convection and oranges signifying suppressed convection, it would seem that storms just east of India fit in best with a Phase 2 or 3 MJO event, seen on the left panels of this graphic above. Considering there has been a link observed between the MJO being in Phase 2 and violent tornado outbreaks occurring consequentially, there is reason to monitor this period for potential severe weather.

The image above shows projected 500mb height anomalies over the northern hemisphere. We can signify the blues with negative height anomalies, which indicate the presence of cooler and stormier weather, while reds denote positive height anomalies, which allow for warmer than normal and calm weather. In the image above, if we look towards the Bering Sea, we can see a very strong ridge of high pressure, seen by the splotch of red around the Aleutian Islands. This image is valid for May 13-14, and if we extrapolate it out 2-3 weeks using the Bering Sea Rule, we can expect high pressure and warm weather to appear in the East US. This extrapolated timeframe looks to fall around the time when this potential severe weather outbreak may strike, and the presence of strong high pressure migrating across the Eastern and Central US may amplify the potential for active weather.

Another device we can use to predict potentially active weather is this grid chart. The dates on the right display the date the forecast was made on, and the dates on the bottom legend indicate when this forecast is valid for. Warmer colors indicate the higher potential for severe weather. For instance, if I want to know the severe weather potential for May 20th on a forecast made on May 5th, I go up the legend on the left to find May 5th, then scroll on the corresponding horizontal line to find the May 20th box. In this case, we have been seeing elevated supercell composite values around the June 15-20 period for some time now, as the red box indicates. This is a long range forecast, but as you can see with severe weather events further to the left on the image, we can get a feel for severe weather potential a long way out, with more accurate forecasts usually coming a few days to a week prior to the event.

This potential event will be updated in coming days as more information becomes available.

Tuesday, May 13, 2014

I'm expecting summerlike warmth to come back for the first week or so of June.

The image above shows projected 500mb height anomalies over the northern hemisphere. We can signify the blues with negative height anomalies, which indicate the presence of cooler and stormier weather, while reds denote positive height anomalies, which allow for warmer than normal and calm weather. In the image above, if we look towards the Bering Sea, we can see a very strong ridge of high pressure, seen by the splotch of red around the Aleutian Islands. This image is valid for May 13-14, and if we extrapolate it out 2-3 weeks using the Bering Sea Rule, we can expect high pressure and warm weather to appear in the East US.

If we look at another 500mb height anomaly forecast graphic, this one valid on May 19th, we now see that our strong ridge has shifted west into the middle of the Bering Sea, with cooler, stormier weather now protruding into western Alaska. This tells us that we can expect warm temperatures in the first several days of June in the middle of the country, with cooler conditions along the Eastern Seaboard.

This warmth is supported by long range modelling of enhanced tropical convection around the central Pacific, which is typically associated with warmer than normal weather in the Central and East US in the May-June-July time period. The bottom panel in the graphic above demonstrates the enhanced convection (blue) present in the Central Pacific.

I'm analyzing the May 21-25 time period for a substantial storm system to bring cool weather and possibly some severe weather to the nation.

Tropical Tidbits

The image above shows projected 500mb height anomalies over the western Pacific. We can signify the blues with negative height anomalies, which indicate the presence of cooler and stormier weather, while reds denote positive height anomalies, which allow for warmer than normal and calm weather. Looking towards Japan on this forecast graphic, valid on May 15th, we see a substantial closed low approaching Japan, bringing in cooler than normal and unsettled weather for the area. If we utilize the Typhoon Rule, we can expect this storm system to impact the United States 6-10 days after this storm affects Japan, which would give us a May 21-25 time period.

Indications I am getting from this graphic tell me much of the United States may be impacted by this cooler than normal weather, and while I do believe severe weather is possible, I'm currently thinking any severe weather will be limited due to the lack of a powerful ridge advecting north over Japan prior to this closed low hitting the country.

Saturday, May 10, 2014

After some consideration, I've decided to create a set of analogs for the upcoming winter, using the same parameters that gave me such high success this past winter.

This post will be divided into two sections of analogs. We will begin with the analog years that matched any two of my five parameters I set forth for this winter.

The image above shows 500mb height anomalies across the northern hemisphere, where cool colors signify stormy and cool weather. Warm colors define the presence of warm and quiet weather. In this image, which shows 500mb height anomalies averaged out across these 9 analog winters, we see significant negative height anomalies across the western coast of North America, defining a textbook negative-Pacific North American index (PNA) pattern. In negative PNA patterns, low pressure dominates the West US, leading to warm weather in the Central and East US. We see ridging in southern Canada, spilling over into the northern United States. There is no clear blocking pattern over the Arctic Circle, meaning cold weather may be even more difficult to come by.

The temperature composite for these same analog years confirms this assumption. We see warm weather dominating the northern United States, maximized in the northern Plains. This sort of temperature pattern is typically associated with an El Nino, where we see warmer than normal weather in the Northern US, with cooler than normal weather in the South or West US.

The precipitation anomaly for these same years confirms the textbook El Nino set-up, as we see below normal precipitation affixed over the southern Ohio Valley down towards the Gulf Coast, and the Southwest US along the Gulf Coast experiencing above normal precipitation. This belt of above normal precipitation looks to be due to the abnormally active subtropical jet stream, another characteristic of an El Nino. We also see a stripe of wetter than normal conditions along the East Coast, which can be attributed to that El Nino-induced subtropical jet stream.

Let's now go over my preferred analogs, which match three of the five chosen parameters that fit the upcoming winter.

Looking at the 500mb height anomaly composite for the four years that match three of my five parameters, we see a much different story than we saw with the less-preferred analog set we just went over. We now see a well-defined blocking situation over the Arctic Circle, with strong positive height anomalies in Greenland and into Canada. This exemplifies the negative phases of the North Atlantic Oscillation (NAO) and the Arctic Oscillation (AO). The negative phases of these indexes both allow cold air to push into the United States, and the negative NAO permits the storm track to push north and threaten the East Coast with more coastal snowstorms.

The temperature composite for these four choice analog years is also a change from the other analog set. Rather than most of the United States being warmer than normal, the negative AO and NAO seem to influence temperatures to be well below normal across much of the nation, maximized in the southern Plains. We still see warmer than normal conditions in the upper Midwest, but these warm anomalies are more restricted than they were in the first analog set. Unfortunately, this could mean the second straight colder than normal winter, as I place more trust in this analog set than the one we first analyzed.

The precipitation composite for these four analog years shows a very stormy East Coast, with anomalies anywhere from 4 to 6 inches above normal, most enhanced in the Southeast. This precipitation pattern is still somewhat aligned with a typical El Nino pattern, though the dryness in the Southeast argues against this somewhat. I'm not as ready to accept this precipitation composite, considering how dominating the El Nino may be this winter, but as always, the analog set will be refined in coming months.

Friday, May 9, 2014

The Japanese Meteorological Agency's long range climate model is predicting a strong El Nino to develop in time for the upcoming winter.

Shown above we see the predicted sea surface temperature (SST) anomalies in the yellow squares from present day to about October 2014, with observed SST anomalies in the red circles on the left side of the graph. We see that the JMA model is predicting a rather linear rise in sea surface temperature anomalies into this summer and fall, reaching El Nino territory by late spring. The shaded red region in this graph indicates the threshold and SST anomalies that define an El Nino (+0.5 degrees C or above), while the blue shaded region defines official La Nina SST anomalies (-0.5 degrees C or below).

The Climate Prediction Center (CPC) here in the United States makes its own climate model as well, named the Coupled Forecast System model (CFS). The CFS model above shows a linear increase in SST anomalies as well, maxing out at around 1.5 degrees Celsius for November-December-January in 2014-2015. The 1.5 degrees C above normal benchmark is also the threshold for a Strong El Nino, meaning such an El Nino of that strength is still possible (though in my personal opinion, not as likely). The general gist of these two models is that we can expect an El Nino to develop later on this summer, likely to strengthen through the fall and into this winter.

Wednesday, May 7, 2014

I'm expecting some cool and stormy weather in mid-May to eventually give way to a shot of above-normal temperatures, before a cool spell returns for late May.

* A quick note, I have had at least 8 comments telling me that my late April-early May forecast was wrong, with more than a couple of these comments delivered with a less-than-enticing attitude. I've been receiving these comments for 2 weeks now- enough is enough. I don't expect myself to be correct 100% of the time, and I certainly hope no one else expects that of me, either.

Tropical Tidbits

The latest GFS Ensemble forecast above, valid on the evening of May 6th, shows troughing and cool weather present over Japan. By using the East Asia / Typhoon Rule, we can estimate that cool and stormy weather is can be expected around May 13-17th or so. Judging by the weak negative 500mb height anomalies, I'm only expecting a weak chill in the US, with the strongest cold weather allocated further north.

Tropical Tidbits

By the morning of May 9th, we see that the western portion of that elongated trough, seen in eastern China on the first image we analyzed, as now become a closed low and is progressing through Japan. If we once again apply this correlation, it is understood that a strong closed low may traverse the United States between a May 15-19th period. When this low comes through, I'm estimating we see it hit primarily the northern and central thirds of the nation, if you were to slice the US into thirds, horizontally. Cooler than normal temperatures can be expected with this, as well.

Tropical Tidbits

We finally do get relief in mid-late May, we a massive ridge of high pressure pumps up over Japan on May 11th, sticking around for a little while. This tells me we can then anticipate a period of anomalously warmer than normal weather in the United States around May 16-22nd or so.

Tropical Tidbits

Unfortunately, long range ensemble guidance supports the return of troughing and associated cold weather in Japan by May 16th, leading to potentially cooler and stormier weather in time for Memorial Day weekend.

Sunday, May 4, 2014

It looks like the much-anticipated El Nino is currently reaching the surface in the eastern Pacific.

Latest sea surface temperature anomalies (SSTAs) over the globe show our El Nino beginning to blossom in the sporadic areas in the waters west of Ecuador. This has been a long time coming, as we have been discussing extensively the Kelvin Wave that has been producing record-breaking temperature anomalies, as high as 6 to 7 degrees C above normal! The wave has been slow to push northward due to a not-as-favorable environment above the surface, but now that we are seeing the El Nino evolve, it can be expected that we will be in at least moderate El Nino territory by the time we hit late autumn.

Mean water temperatures along the equator from the surface to 500 meters down (top),
and anomalies for the same cross-section region (bottom).

If we take a look at sea surface temperature anomalies, now diagnosed on a cross-section along the equator from the surface to 500 meters down, it is evident that this Kelvin Wave-produced warm water is quickly upwelling to the surface. We see anomalies as high as 6 degrees C above normal about fifty meters below the surface, as is seen on the bottom panel in the top-right corner. As this body of warm water continues to push to the surface, we will likely see gradual weakening of these anomalies, but they should still be strong enough to propel us into our first El Nino event in multiple years.

Saturday, May 3, 2014

It's looking more like we can expect a severe weather threat around the May 7th-8th period.

Tropical Tidbits

(The following is copied from a May 1st post) On the afternoon of May 2nd, we see a small but still-substantial ridge of high pressure pushing over Japan, as a strong storm system to the west begins pushing in the direction of the island nation. There is a rule, well explained by Joe Renken, that states a weather phenomenon in East Asia will be reciprocated in the United States 6-10 days later. This means that if there is a storm system in Japan on a certain day, we can expect a storm in the US 6-10 days after that. The same goes for high pressure and warm weather. Seeing as this ridge appears on May 2nd in Japan, we can expect some warm weather around May 8-12th.

Tropical Tidbits

By May 3rd, we see a strong storm pushing into Japan in the wake of the ridge we saw in the image above. Looking at the trough, it looks like the system is negatively tilted, as seen by the pressure contours pushing in a south-east direction. If this trough reflects on the United States in about a week, which it very well may, the negative tilt may result in a pretty substantial severe weather threat. Locations of this threat are unknown at this time, but be cautious for some severe weather in this timeframe. (End copied portion)

The Storm Prediction Center has outlined an area of enhanced severe weather risk on May 8th from Oklahoma into southern Wisconsin. This threat area includes cities such as Chicago IL, Milwaukee WI, and Wichita KS, just to name a few.

The surface analysis forecast from the Weather Prediction Center for May 8th shows a strong low pressure system moving northeast into Minnesota, dragging a warm front to the north, which should allow for a warm, moist and unstable atmosphere to flow over the area. To the west, we see a cold front draped across the Central and Southern Plains, with a dryline denotation in western Oklahoma and Texas. I expect that we will see the cold front be the main cause for this severe weather event, while the dryline to the south may provoke additional activity in the southern Plains. I anticipate the highest tornado threat to remain in the southern Plains, as dryline features typically can retain more tornadic cells than cold fronts, but we will analyze that idea later on. The Storm Prediction Center indicates we can expect the main threats to include damaging winds and hail, with a tornado threat still present, as is indicated below.

AS MODELS BRING THE UPPER TROUGH EWD INTO THE PLAINS DAY 6 /THU 5-8/ HOWEVER...MORE COMPLETELY MODIFIED GULF MOISTURE APPEARS LIKELY TO HAVE SPREAD INTO THE CENTRAL U.S. PERMITTING DEVELOPMENT OF MORE SUBSTANTIAL CAPE. AS THE SURFACE LOW SHIFTS NEWD ALLOWING A TRAILING FRONTAL ADVANCE ACROSS THE CENTRAL PLAINS VICINITY...DEVELOPMENT OF AFTERNOON SURFACE-BASED STORMS APPEARS LIKELY. WITH THE GREATEST JUXTAPOSITION OF FAVORABLE SHEAR AND MODERATE CAPE LIKELY TO EXIST FROM ROUGHLY OK NEWD ACROSS KS/MO/IA AND INTO IL AND SRN WI...IT APPEARS THAT INCLUSION OF A 30 PERCENT-EQUIVALENT RISK AREA CAN BE INTRODUCED ATTM WITH MODERATE CONFIDENCE...WITH HAIL/DAMAGING WINDS LIKELY ALONG WITH SOME TORNADO POTENTIAL.

I do believe we may see another severe weather outlook posted for May 7th for areas further to the west, as we take a look at rank-analog tornado probabilities off of the GEFS modeling system. Out of the four panels, the one which highlights the overall tornado probability is in the top-left corner, and we can see in that panel that Nebraska and Kansas may be in line for as high as a 10% chance of a tornado, which would certainly warrant a severe weather outlook.

If we take a look at the same four-panel forecast image, now valid on May 8th, we can see how the Storm Prediction Center is highlighting areas in Oklahoma into Wisconsin. It appears that the tornado threat here is weaker and displaced farther west than the SPC outlook for this day, but as was mentioned earlier, the main threats should be damaging winds and hail. I find that the threat for this day is more accurately highlighted in the other three panels, which calculate different values for ingredients of severe weather and general thunderstorms.Overall, we are looking at a severe weather threat on May 8th (and potentially May 7th) over the Plains and Midwest regions.Andrew

Thursday, May 1, 2014

On the afternoon of May 2nd, we see a small but still-substantial ridge of high pressure pushing over Japan, as a strong storm system to the west begins pushing in the direction of the island nation. There is a rule, well explained by Joe Renken, that states a weather phenomenon in East Asia will be reciprocated in the United States 6-10 days later. This means that if there is a storm system in Japan on a certain day, we can expect a storm in the US 6-10 days after that. The same goes for high pressure and warm weather. Seeing as this ridge appears on May 2nd in Japan, we can expect some warm weather around May 8-12th.

Tropical Tidbits

By May 3rd, we see a strong storm pushing into Japan in the wake of the ridge we saw in the image above. Looking at the trough, it looks like the system is negatively tilted, as seen by the pressure contours pushing in a south-east direction. If this trough reflects on the United States in about a week, which it very well may, the negative tilt may result in a pretty substantial severe weather threat. Locations of this threat are unknown at this time, but be cautious for some severe weather in this timeframe.

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